Ventricular assist devices (VADs) include blood pumps, which are used to help patients who suffer from poor blood circulation and heart disease. VAD can be implanted in the patient's body to assist the heart and provide improved blood circulation. An implanted VAD may be powered by an electrical power source located outside of the patient's body. Power is transmitted from the electrical power source to the implanted VAD via percutaneous cable.
An implanted VAD is powered and controlled by electronic components. It is also desirable to place such electronic components inside the human body so that the temperature shift can be significantly reduced. Also, placing such electronic components inside the human body facilitates a reduced number of leads inside the cable. This reduces the size of the cable and helps to improve reliability of the system when the cable is subject to wear, fatigue and other damages due to mistaken handling of the cable by patients. A further advantage to reduce the number of leads in the cable is to improve electromagnetic compatibility since the cable is exposed to electromagnetic interference from the environment, but electronics inside the human body does not.
A conventional blood pump in a VAD is driven by one or more three-phase electric motors such as a brushless direct current (DC) three-phase motor or an alternating current (AC) type three-phase motor. The motor's windings receive electric currents from power electronics. In conventional practice, the power electronics are configured outside of the blood pump, so at least three leads (wires), which correspond to the three phases of the pump motor, are used in the percutaneous cable to connect the power electronics outside of the pump and the motor windings inside the pump.
Some conventional VADs include a pump rotor configuration which employs magnetic suspension (i.e., magnetic bearings) for the rotor. A magnetic suspension system is used to stabilize one or more degrees of freedom of the rotor. For each degree of freedom, a feedback loop incorporates a sensor, which detects the position of the rotor, a controller, which receives signal from the sensor and then generates a control signal through sophisticated signal processing, and a power electronics unit, which generates electric current following the command of the control signal. The electric current then flows into the windings in the magnetic bearing to create magnetic force on the rotor.
Conventionally, both the controller and the power electronics are placed outside of the blood pump. Additional leads within percutaneous cable are used to feed the position sensor signal from inside the pump to the controller outside of the pump. Additional leads within percutaneous cable are used to connect the power electronics outside of the pump to the magnetic bearing windings inside the pump. That means at least four leads are required if one degree of freedom of the rotor is stabilized by the magnetic bearing. More leads are required if more than one degree of freedom are actively controlled by magnetic bearings.
The use of a VAD involves subjecting a patient to certain risks including the risk of infection at the site where the percutaneous cable penetrates the skin. To reduce the risk of infection, it is desirable to have percutaneous cable as small and flexible as possible. Therefore, it is desirable to reduce the number of leads inside the percutaneous cable.
It should be understood that the comments included in the notes as well as the materials, dimensions and tolerances discussed therein are simply proposals such that one skilled in the art would be able to modify the proposals within the scope of the present disclosure.